A wide variety of personal care and cosmetic products are essentially oil-in-water (O/W) emulsions, comprising finely divided oil droplets dispersed homogeneously in an aqueous solution. The commonly used oils or oil like substances range from various esters and triglycerides to various hydrocarbons and silicone fluids. These emulsions may contain high levels of active benefit agents intended to deliver skin care, hair care, and other benefits. Many of these agents are electrolytic and/or acidic compounds which pose considerable challenges towards maintaining good stability of the emulsions during their storage. Stabilizing these emulsions against separation of the oil phase (coalescence) or agglomeration (flocculation) of emulsion droplets, when the emulsions contain high levels of electrolytes, and/or have an extreme pH, would require the use of a highly effective emulsifier.
Surface active polymers (or polymeric surfactants) that are capable of adsorbing at an oil/water interface typically perform more efficiently than low molecular weight surfactants, as an emulsifier. Generally, once polymers adsorb onto and thus coat the surface of emulsion droplets, they can provide for a strong, long range droplet-to-droplet repulsion, known as steric repulsion in the art, which in turn prevents the emulsion droplets from closely approaching one another, in effect, stabilizing the droplets against flocculation and coalescence.
Synthetic and semi natural polymeric emulsifiers are widely used in overcoming the aforementioned challenges in formulating stable emulsions for personal care and cosmetic products. A vast majority of the synthetic polymeric emulsifiers in use today are esterified polyethoxylated polymers, an example of which is PEG-100 stearate. The semi natural polymeric emulsifiers are derived from naturally occurring polyols, such as sugars, glycerides and saccharides, which are subsequently modified by ethoxylation and/or lipophilic esterification, e.g., ethoxylated methyl glucose esterified with a fatty acid. However, a serious health concern surrounds these PEG containing ingredients, ever since it became known that ethoxylated materials can generate the highly toxic substance, 1,4-dioxane, in their manufacture.
Oil-in-water (O/W) emulsions formulated into personal care and cosmetic products typically contain polymeric thickening agents in the water phase of the emulsion. When a polymeric surfactant is used as an emulsifier, an amount of the polymer adsorbs onto the surface of the emulsion droplet, while the rest (free or unadsorbed) remains dissolved in the water phase, maintaining a thermodynamic equilibrium between the adsorbed and free polymer. The higher the concentration of the polymer, the higher the amount of the free polymer that is present in the solution phase. The polymeric emulsifier possibly can interact with the polymeric thickening agent, for example, via hydrogen bonding and/or hydrophobic interactions, such interpolymer interactions in some cases could potentially reduce the efficacy of the thickening agent.
A way to avoid the foregoing problem is to formulate emulsions that have relatively large sized droplets, while maintaining good emulsion stability. It is, however, generally more difficult to stabilize large emulsion droplets against flocculation because the larger the emulsion droplet, the stronger the van der Waals attraction acting between them. This ubiquitous inter-droplet attraction tends to oppose any inter droplet repulsion instilled, for example, through the use of a polymeric emulsifier. For a given weight of an emulsified oil phase, larger emulsion droplets would present a lower total (interfacial) surface area to be coated by the emulsifier. Accordingly, the larger the size of an emulsion droplet, a lower emulsifier dosage may be required for effecting good emulsion stability ameliorating any adverse effects of an emulsifier/thickener interaction.
Furthermore, it is often desirable in the manufacturing of personal care products that highly concentrated O/W emulsions are produced first in stable and pumpable (i.e., not overly viscous) forms, which can be stored for a period of time (generally as long as several days or weeks) before they are diluted with additional ingredients for producing the final product. Clearly, it is critical that such concentrated emulsions remain stable against flocculation and coalescence, and retain a pumpable consistency during and after the storage period.
It is often challenging to produce stable O/W emulsions, if the amount of the oil phase exceeds 55 to 60 wt. % of the emulsion. Also, even when free of any thickening agent, O/W emulsions can be highly viscous if the emulsion droplets undergo extensive flocculation (wherein an amount of the water phase gets entrapped within the flocs and is no longer available to impart fluidity to the emulsion). Furthermore, in concentrated emulsions, the smaller and the more uniform the size of the emulsion droplets, the higher is the emulsion viscosity. Hence, a way to provide highly concentrated yet low viscosity emulsions is to produce emulsions with a relatively large droplet size, while ensuring that the droplets are substantially stable against flocculation.
The recent consumer demand for personal care products to be derived from naturally sourced ingredients, given that their use involves bodily contact have led product formulators to include vegetable oils as the oil phase component in O/W emulsions. However, emulsifying these oils, which are primarily composed of triglycerides, into stable emulsions is challenging. The aforementioned polyethoxylated emulsifiers are very effective emulsifiers for these oils. While the semi natural emulsifiers include naturally sourced components, they are increasingly seen as less sustainable because of the use of petrochemically derived ethylene oxide in their manufacture. Moreover, because of the health and safety concerns associated with ethoxylated materials, there is a growing need for ethoxylate free emulsifiers that provide efficient and stable emulsification of oil phase components, particularly when vegetable oils are utilized as the oil phase.
For the foregoing reasons, it would be beneficial to provide an emulsifier that is substantially derived from naturally sourced materials and free of toxic contaminants for use in products formulated as O/W emulsions. It also would be beneficial to deliver an emulsifier with the properties described above, that could be successfully used in stabilizing O/W emulsions of natural oils such as vegetable derived oils.
To the best of our knowledge, such a desirable emulsifier for O/W emulsions (particularly in personal care and cosmetic product emulsions) has not been disclosed in the art. Accordingly, there is a need for an emulsifier that meets the foregoing parameters.